Detector constructed from fabric having planes with differing conductance

ABSTRACT

A position detector is constructed from fabric having electrically conductive elements. The detector has at least two electrically conductive planes. An electrical potential is applied across one of the planes to determine the position to a mechanical interaction. In addition, second electrical property is determined to identify additional properties of the mechanical interactions.

RELATED APPLICATION

This is a division of my copending commonly assigned application Ser.No. 09/298,172 filed Apr. 23, 1999.

FIELD OF THE INVENTION

The present invention relates to a detector constructed from fabrichaving electrically conductive elements to define at least twoelectrically conductive planes.

INTRODUCTION TO THE INVENTION

A fabric touch sensor for providing positional information is describedin U.S. Pat. No. 4,659,873 of Gibson. The sensor is fabricated using atleast one resistive fabric layer in the form of conducting threads. Thisfabric is constructed using either uni-directional threads or crossedthreads formed by overlaying one set with another or weaving the twosets together. The fabric is separated from a second resistive layer toprevent unintentional contact by separators in the form ofnon-conducting threads, insulator dots or with an air gap. Bothresistive layers are fabrics formed from conductive threads such that nopre-forming is required in order to adapt the sensor to a contouredobject.

A problem with the sensor described in the aforesaid United Statespatent is that it is only capable of identifying the location of themechanical interaction and cannot provide additional information aboutthe interaction.

A touch sensor for providing positional information is described in U.S.Pat. No. 4,487,885 of Talmage, which also provides a signal dependentupon the pressure or force applied. However, the sensor described ismade from a printed circuit board and a flexible sheet of rubber,elastomer or plastic and as such it does not have the many physicalqualities that a fabric may provide.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda position detector constructed from fabric having electricallyconductive elements, comprising at least two electrically conductingplanes, wherein an electric potential is applied across at least one ofsaid planes to determine the position of a mechanical interaction; and asecond electrical property is determined to identify additionalproperties of said mechanical interaction.

In a preferred embodiment, the position detector is configured tomeasure current or resistance as said second electrical property.Furthermore, applied force, applied pressure, area of contact ororientation of an object may be determined as the additional property ofmechanical interactions.

In a preferred embodiment, the detector interacts mechanically withparts of a human body; a first electrical property determines theposition of a mechanical interaction and a second electrical propertydetermines the area of coverage.

According to a second aspect of the present invention, there is provideda method of detection, performed with respect to a detector constructedfrom fabric and having electrically conductive elements configured toprovide at least two electrically conducting planes, comprising thesteps of applying a potential across at least one of said planes todetermine the position of a mechanical interaction, and measuring asecond electrical property to identify additional properties of saidmechanical interactions.

According to a third aspect of the present invention, there is provideda detector constructed from fabric having electrically conductiveelements and configured to produce electrical outputs in response tomechanical interactions, wherein said detector is divided into aplurality of regions; each of said regions includes a first conductingplane and a second conducting plane; a mechanical interaction results inconducting planes of at least one of said regions being brought closertogether; and a potential is applied across at least one of said planesto determine the position of said mechanical interaction.

According to a fourth aspect of the present invention, there is provideda detector constructed from fabric having electrically conductiveelements to define at least two electrically conducting planes andconfigured to produce an electrical output in response to a mechanicalinteraction, wherein a potential is applied across at least one of saidplanes to determine the position of a mechanical interaction and saidsecond electrical property is determined to identify additionalproperties of said mechanical interactions; and a conductivitynon-uniformity is included in at least one of said planes so as tomodify an electrical response to a mechanical interaction.

In a preferred embodiment, the conductivity non-uniformity includes aco-operating pair of conducting strips configured to generate asubstantially linear electric field within the conducting planes.Preferably, the strips are applied to each of the conducting planes atorthogonal locations.

According to an alternative preferred embodiment, all edges of theconducting planes are modified. The conductivity non-uniformity may bedefined by adjusting the density of conducting threads or it may becreated by printing conductive materials onto the detector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a position detector constructed from fabric;

FIG. 2 shows a control circuit identified in FIG. 1;

FIG. 3 details operations performed by the micro-controller identifiedin FIG. 2;

FIG. 4 details planes identified in FIG. 1;

FIG. 5 details current flow due to mechanical interaction;

FIGS. 6A-6D detail an alternative construction for conducting fabricplanes;

FIG. 7 shows an alternative configuration of conducting planes;

FIGS. 8A-8D show an alternative configuration of conducting planes;

FIG. 9 details a composite configuration of conducting planes; and

FIGS. 10A-10B show an asymmetric object interacting with conductingplanes;

FIG. 11A and FIG. 11B show an alternative construction for a detector;

FIG. 12A and FIG. 12B show a further alternative construction;

FIG. 13 shows a further alternative construction;

FIG. 14 shows a further alternative construction.

FIG. 15 shows an alternative embodiment having a plurality of detectors;

FIG. 16 shows an alternative detector configuration; and

FIGS. 17A-17B show multiple detectors of the type shown in FIG. 16;

FIG. 18 shows a first embodiment in which a connector has been includedduring the machining process; and

FIG. 19 shows an alternative embodiment in which a connector has beenadded during a machining process.

FIG. 20 shows a detector constructed from fabric having a conductivitynon-uniformity; and

FIG. 21 shows an alternative embodiment with a conductivitynon-uniformity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described by way of example only withreference to the previously identified drawings.

A position detector 101 constructed from fabric is shown in FIG. 1. Thedetector has two electrically conducting fabric planes, in the form of afirst plane 102 and a second plane 103. The planes are separated fromeach other and thereby electrically insulated from each other, by meansof an insulating mesh 104. When force is applied to one of the planes,the two conducting planes are brought together, through the mesh 104,thereby creating a position at which electrical current may conductbetween planes 102 and 103. In this way, it is possible to identify theoccurrence and/or position of a mechanical interaction.

The fabric planes are defined by fabric structures, which may beconsidered as a woven, non-woven (felted) or knitted etc. The fabriclayers may be manufactured separately and then combined to form thedetector or the composite may be created as part of the mechanicalconstruction process.

When a voltage is applied across terminals 107 and 108, a voltagegradient appears over plane 102. When a mechanical interaction takesplace, plane 103 is brought into electrical contact with plane 102 andthe actual voltage applied to plane 103 will depend upon the position ofthe interaction. Similarly when a voltage is applied between connectors111 and 112, a voltage gradient will appear across plane 103 andmechanical interaction will result in a voltage being applied to plane102. Similarly, the actual voltage applied to plane 102 will depend uponthe actual position of the interaction. In this way, for a particularmechanical interaction, it is possible to identify locations within theplane with reference to the two aforesaid measurements. Thus, connectors107, 108, 111 and 112 are received by a control circuit 121, configuredto apply voltage potentials to the detector 101 and to make measurementsof electrical properties in response to mechanical interactions.

Control circuit 121 identifies electrical characteristics of the sensor101 and in response to these calculations, data relating to thecharacteristics of the environment are supplied to a data processingsystem, such as a portable computer 131, via a conventional serialinterface 132.

Control circuit 121 is detailed in FIG. 2. The control circuit includesa micro-controller 201 such as a Philips 80C51 running at a clockfrequency of twenty megahertz. Operations performed by micro-controller201 are effected in response to internally stored commands held by aninternal two kilobyte read-only memory. The micro-controller alsoincludes one hundred and twenty-eight bytes of randomly accessiblememory to facilitate intermediate storage while performing calculations.Micro-controller 201 includes a serial interface 202 in addition toassignable pins and an interface for communicating with an analogue todigital converter 203, arranged to convert input voltages into digitalsignals processable by the micro-controller 201.

The control circuit 121 includes two PNP transistors 211 and 212, inaddition to four NPN transistors 213, 214, 215 and 216. All of thetransistors are of relatively general purpose construction and controlswitching operations within the control circuit so as to control theapplication of voltages to the position detector 101.

In operation, measurements are made while a voltage is applied acrossfirst plane 102 and then additional measurements are made while avoltage is applied across the second plane 103; and output voltage onlybeing applied to one of the planes at any particular time. When anoutput voltage is applied to one of the planes, plane 102 or plane 103,input signals are received from the co-operating plane 103 or 102respectively. Input signals are received by the analogue to digitalconverter 203 via a selection switch 221, implemented as a CMOS switch,in response to a control signal received from pin C6 of themicro-controller 201. Thus, in its orientation shown in FIG. 2, switch221 has been placed in a condition to receive an output from a firsthigh impedance buffer 222, buffering an input signal received from plane102. Similarly, when switch 221 is placed in its alternative condition,an input is received from a second high impedance buffer 223, configuredto receive an input signal from plane 103. By placing buffers 222 and223 on the input side of CMOS switch 221, the switch is isolated fromhigh voltage electrostatic discharges which may be generated in manyconditions where the detector undergoes mechanical interactions.

In the condition shown in FIG. 2, switch 221 is placed in its uppercondition, receiving input signals from buffer 222, with output signalsbeing supplied to the second plane 103. Further operation will bedescribed with respect to this mode of operation and it should beappreciated that the roles of the transistor circuitry are reversed whenswitch 221 is placed in its alternative condition. As previously stated,condition selection is determined by an output signal from pin C6 ofmicro-controller 201. In its present condition the output from pin C6 islow and switch 221 is placed in its alternative configuration when theoutput from pin 6 is high.

Output pin CO controls the conductivity of transistor 211 with pins Clto C5 having similar conductivity control upon transistors 213, 214,212, 215 and 216 respectively.

Transistors 211 and 213 are switched on when a voltage is being appliedto the first plane 102 and are switched off when a voltage is beingapplied to the second plane 103. Similarly, when a voltage is beingapplied to the second plane 103, transistors 212 and 215 are switched onwith transistors 211 and 213 being switched off. In the configurationshown in FIG. 2, with switch 221 receiving an input from buffer 222,output transistors 211 and 213 are switched off with output transistors212 and 215 being switched on. This is achieved by output pin C0 beingplaced in a high condition and pin C1 being placed in a low condition.Similarly, pin C3 is placed in a low condition and pin C4 is placed in ahigh condition.

In the configuration shown, C3 is placed in a low condition, aspreviously described. The micro-controller 201 includes a pull-downtransistor arranged to sink current from the base of transistor 212,resulting in transistor 212 being switched on to saturation.Consequently, transistor 212 appears as having a very low resistance,thereby placing terminal 111 at the supply voltage of five volts.Resistor 231 (4K7) limits the flow of current out of themicro-controller 201, thereby preventing burn-out of themicro-controller's output transistor.

Pin C4 is placed in a high state, resulting in transistor 215 beingplaced in a conducting condition. A serial resistor is not requiredgiven that the micro-controller 201 includes internal pull-up resistors,as distinct from a pull-up transistor, such that current flow isrestricted. Thus, transistors 212 and 215 are both rendered conductive,resulting in terminal 111 being placed at the positive supply railvoltage and terminal 112 being placed at ground voltage. The capacitorsshown in the circuit, such as capacitor 219, limit the rate oftransistor transitions thereby reducing rf transmissions from the sensor101.

With transistors 212 and 215 placed in their conductive condition, inputsignals are received from the first plane 102 in the form of a voltageapplied to terminal 108. For position detection, this voltage ismeasured directly and transistor 214 is placed in a non-conductivecondition by output pin C2 being placed in a low condition. Under theseconditions, the voltage from input terminal 108 is applied to analogueto digital converter 203 via buffer 222 and switch 221.

In accordance with the present invention, a second electrical propertyis determined which, in this embodiment, represents the current flowingthrough the sensor in response to a mechanical interaction. The currentmeasurement is made by placing transistor 214 in a conductive condition,by placing output pin C2 in a high condition. In this condition, currentreceived at terminal 108 is supplied to transistor 214 via resistor214A, having a resistance of typically 5 k selectable so as tocorrespond to the characteristics of the sensor. A voltage is suppliedto A to D converter 203 via buffer 222 and switch 221 but on thisoccasion the voltage represents a voltage drop, and hence a current,across resistor 214A.

Thus, transistors 212 and 215 are placed in a conducting condition,transistor 214 is placed in a non-conducting condition, so as to measurevoltage, and is then placed in a conducting condition so as to measurecurrent. The roles of the transistors are then reversed, such thatoutput transistors 211 and 213 are placed in a conducting condition,with transistors 212 and 215 being placed in a non-conducting condition(and switch 221 reversed) allowing a voltage to be measured by placingtransistor 216 in a non-conducting condition, and then allowing acurrent to be measured by placing transistor 216 in a conductingcondition.

The cycling of line conditions, in order to make the measurementsidentified previously, is controlled by a clock resident withinmicro-controller 201. After each condition has been set up, a twelve bitnumber is received from the digital to analogue converter 203 and thisnumber is retained within a respective register within micro-controller201. Thus, after completing a cycle of four measurements, four twelvebit values are stored within the micro-controller 201 for interrogationby the processing device 131. Furthermore, the rate of cycling may becontrolled in response to instructions received from the processingdevice 131.

Operations performed by micro-controller 201 are detailed in FIG. 3. Themicro-controller continually cycles between its four configurationstates and each time a new input is produced, representing a current ora voltage in one of the two configurations, new output data iscalculated on an on-going basis. Thus, output registers are updated suchthat the best data is made available if the micro-controller isinterrupted by the external processor 131.

The micro-controller 201 is fully interrupt driven in terms of receivingexternal interrupts for data interrogation along with internalinterrupts in order to initiate a configuration cycle. The externalinterrupt has a higher priority such that external processor 131 isprovided with information as soon as possible in response to making aninterrupt request.

Internally interrupts for the micro-controller 201 are generated by itsown internal timer and the procedure shown in FIG. 3 is effectively heldin a wait state until a next timer interrupt is received at step 301.The wait state allows voltage levels on connections 107, 108, 111 and112 to become stable and provides sufficient time for valid data to bereceived from the analogue to digital converter 203.

At step 302, an output is received from analogue to digital converter203 and at step 303 calculations are performed with respect to the mostcurrent data received from the analogue to digital converter, so as toconvert numerical values relating to voltages and currents intonumerical values representing properties of the mechanical interaction.Thus, after performing calculations at step 303, appropriate registersare updated at step 304 and it is these registers that are interrogatedin response to an interrupt received from processing system 131.

At step 305 next conditions for the output lines are set by appropriatelogic levels being established for output pins C0 to C6. After the nextoutput condition has been selected, the processor enters a wait state atstep 306, allowing the electrical characteristics to settle, whereafterprocessing continues in response to the next timer interrupt.

Thus, it should be appreciated that on each iteration of the procedureshown in FIG. 3, one of the output conditions is selected at step 305.Thus, it should be appreciated that the input data is effectivelydelayed and does not represent a condition of the electricalcharacteristics at an instant. If in practice, the delay betweenmeasurements becomes too large, it becomes necessary to enhance thefrequency of operation of circuits within the control system shown inFIG. 2. Thus, the rate of conversion for converter 203 would need to beincreased and the circuitry would need to be redesigned for highfrequency operation. This in turn could create problems in terms of highfrequency interference resulting in enhanced shielding being requiredfor the facility as a whole.

When output condition number one is selected, an output voltage at 108is determined. On the next cycle, identified as output condition numbertwo, the current flowing through connector 108 is determined. On thenext iteration, under output configuration number three, the voltageappearing at connector 112 is determined and on the next cycle,identified as condition number four, the current flowing throughconnector 112 is determined. After each of these individualmeasurements, new data is generated in response to steps 303 and 304such that resulting output registers are being regularly updated on acontinual basis, such that the processing system 131 may effectivelyperform a continual monitoring operation in terms of changes made to themechanical interactions with the detector 101.

In a typical implementation, the four characteristic measurements,making up a complete cycle, will be repeated at a frequency of betweentwenty-five to fifty times per second. In situations where such arepetition rate is not required, it may be preferable to increase theduration of the wait states and thereby significantly reduce overallpower consumption.

Planes 102, 103 and 104 of the detector 101 are detailed in FIG. 4.Planes 102 and 103 are of substantially similar construction and areconstructed from fabric having electrically conductive elements 402 inplane 102 along with similar electrical conductive elements 403 in plane103. Thus, it is possible for a voltage indicative of position to bedetermined when conductive elements 402 are placed in physical contactwith conductive elements 403.

The overall resistivity of planes 102 and 103 are controlled by theinclusion of non-conducting elements 404 and 405. Thus, resistivity iscontrolled by controlling the relative quantities and/or densities ofconductive elements 402 with non-conductive elements 404. Resistivitymay also be controlled by selecting an appropriate fibre type, adjustingthe thickness of the fibre or adjusting the number of strands present ina yarn.

Plane 104 represents a non-conducting insulating spacer positionedbetween the two conducting planes 102 and 103. Plane 104 is constructedas a moulded or woven nylon sheet having an array of substantiallyhexagonal holes 411, the size of holes 411 is chosen so as to controlthe ease with which it is possible to bring conductive elements 402 intophysical contact with conductive elements 403. Thus, if relatively smallholes 411 are chosen, a greater force is required in order to bring theconductive elements together. Similarly, if the size of the hole isincreased, less force is required in order to achieve the conductiveeffect. Thus, the size of holes 411 would be chosen so as to provideoptimal operating conditions for a particular application. Operatingconditions may also be adjusted by controlling the thickness of layer104, its surface flexibility and the contour of co-operating planes 102and 103.

When a potential is applied across one of the conducting planes, theactual potential detected at a point on that plane will be related tothe position at which the measurement is made. Thus, a direct voltagemeasurement from the co-operating plane gives a value from which apositional co-ordinate may be determined. By reversing the role of theplanes and taking a measurement from the opposing plane, twoco-ordinates are obtained from which it is then possible to identify aprecise location over the planar surface.

In addition to measuring position on the planar surface, the presentinvention is directed at identifying additional electrical properties inorder to determine properties of the mechanical interaction. Aspreviously described, the system is configured to measure currents inaddition to measuring voltages.

When the two conducting planes are brought into mechanical contact, dueto a mechanical interaction, the amount of current flowing as a resultof this contact will vary in dependence upon the actual position of theplane where the mechanical interaction takes place. The position of themechanical interaction has also been determined with reference tovoltages and it could be expected that these two quantities will vary ina substantially similar way, each representing the same physicalsituation. Experience has shown that variations in measured current donot follow exactly the same characteristic as variations in measuredvoltage. As illustrated in FIG. 5, the amount of current flowing due toa mechanical interaction will depend upon the position of a mechanicalinteraction 501. However, in addition to this, the amount of currentflow will also depend upon the size of the mechanical interaction. Asthe size of the mechanical interaction increases, there is a greaterarea of contact and as such the overall resistance of the mechanicalinteraction is reduced. However, it should be appreciated thatvariations in terms of current with respect to interaction size is asophisticated relationship, given that, in addition to the resistivityof the contact area 501, the resistivity of the actual electricalconnections within the sheet must also be taken into account.

Thus, current is transmitted through a region 502 in order to provide acurrent to the contact region 501. Some aspects of this effect will becompensated with reference to position calculations and other variationsdue to this effect may be compensated by a non-linear analysis of theinput data.

Contact area resistivity is illustrated generally at 510 and shows thatthe amount of current flowing between plane 102 and plane 103 isconsidered as being related to the area of mechanical interaction, whichis related to the area of contact externally and to the level ofexternally applied mechanical force.

The resulting non-linear relationship between the force area product andthe resulting current flow is illustrated generally at 520. At 521 thereis an initial threshold point, identifying the point at which the gapstarts to be closed, followed by an operational part of the curve 522which may give useful indications of pressure up to point 523,whereafter the relationship becomes very non-linear until position 524where the relationship effectively saturates.

Using a detector of the type illustrated in FIG. 1, it is possible tomeasure current flow, which could also be considered as contactresistance, in order to identify an additional mechanical property ofthe interaction. As illustrated in FIG. 5, this other mechanicalproperty is related to the area of contact between the sheets,determined by the amount of force applied to the sheets, and to thetotal area over which the force is applied; or a combination of thesetwo properties. Thus, data relating to force and area may give usefulinformation relating to the interaction, separate from the position atwhich the interaction takes place.

In some situations, such as when using a stylus or similar implement,the area of applied force remains substantially constant therefore ameasurement of current will enable calculations to be made in terms ofstylus pressure. Pressure sensitive styli are known but in knownconfigurations the pressure detection is determined within the stylusitself, leading to the stylus being mechanically connected tooperational equipment or requiring sophisticated wireless transmissionwithin the stylus itself. The present embodiment allows stylus pressureto be determined using any non-sophisticated stylus, given that thepressure detection is made by the co-operating fabric detector, arrangedto detect stylus position (with reference to voltage) in combinationwith stylus pressure, with reference to current.

An alternative construction for the conducting fabric planes isillustrated in FIGS. 6A-6D. The detector includes a first conductingplane 601 and a second conducting plane 602. In addition, woven intoeach of the conducting planes 601 and 602, there are a plurality ofnon-conducting nodes 605 arranged to mutually interfere and therebyseparate the two conducting planes. Between the nodes, the fabrics ofthe first and second planes may be brought into contact relativelyeasily such that the application of force, illustrated by arrow 611(FIG. 6B) would tend to cause a finite number of regions interspersedbetween nodes 605 to be brought into contact. Thus, for a particularregion, contact either is taking place or is not taking place asillustrated by curve 621 (FIG. 6C).

With a number of such regions brought into contact, the overall level ofcurrent flow will tend to vary with the area of contact as illustratedby curve 631 (FIG. 6D). Thus, using a construction of the type shown inFIG. 6A, it is possible to obtain a more linear relationship, comparedto that shown in FIG. 5, in which the level of current flow gives a verygood indication of the area of coverage as distinct from the level offorce applied to the mechanical interaction.

Given a construction of the type shown in FIG. 6A, an indication ofapplied force or pressure may be obtained, in addition to an accuratedetermination of area, by providing an incremental switching operation.In the configuration shown in FIG. 7, there is provided a firstconducting plane 701 which interacts with a second conducting plane 702.Furthermore, conducting plane 702 interacts with a third conductingplane 704. Conducting plane 701 is separated from conducting plane 702by non-conducting portions 705. Similarly, plane 702 is separated fromplane 704 by non-conducting portions 706. More non-conducting portions706 are provided than similar non-conducting portions 705. Consequently,less force is required to produce electrical contact between planes 701and 702 than is required to produce an electrical contact between planes702 and 704. In this way, it is possible to provide an incrementalmeasurement of force, given that a low force will only cause contactbetween plane 701 and plane 702 whereas a larger force will also provideelectrical contact between plane 702 and 704.

An alternative configuration is shown in FIG. 8A in which it is possibleto obtain enhanced substantially continuous variations in current flowwith respect to applied force. A first conducting plane 801 interactswith a second conducting plane 802. The planes are woven in such a wayas to produce very uneven surfaces such that, under light load, thelevel of interaction is relatively low. As load increases, asillustrated generally at 805 (FIG. 8B), a greater level of surfacecontact shown at 806 is created thereby increasing the level of currentflow in a substantially continuous way. It should also be noted thatthis configuration does not include an insulating layer as such and thata level of current flow will always take place even under conditions ofzero load. Alternatively, a very thin insulating layer could beprovided, having a relatively low threshold, thereby resulting in a zerocurrent flow when no load is applied.

As shown by curve 811 (FIG. 8C), the output current varies with respectto variations in applied force for a constant load area. Similarly, asshown by curve 821 (FIG. 8D), output current varies with respect to loadarea for a substantially constant applied force.

A composite configuration is shown in FIG. 9, in which a detector 901,substantially similar to that shown in FIG. 6, is combined with adetector 902, substantially similar to that shown in FIG. 9. Detector901 provides an accurate measurement of applied area and it isrelatively unaffected by applied force. Detector 902, as shown in FIG.8, provides an output which varies with respect to area and force. Thus,by processing the output of these two detectors in combination, it ispossible to compensate the output from detector 902 in order to producevalues representing force, such that the two currents provideindications of both force and area.

The operation of the control circuit 121 is such as to apply a firstvoltage across diagnoals 107 and 108 with a similar voltage beingapplied across diagnoals 111 and 112. The nature of the voltagedistribution is therefore asymmetric, but this does not result indifficulties provided that the area of contact between the two planes isrelatively symmetric. However, should an asymmetric area of contact bemade, as illustrated in FIGS. 10A and 10B, differences will occur interms of current measurements when considering calculations made in thetwo directions.

An asymmetric object 1001 is shown applied to the surface of a detector1002. When a voltage is applied between contact 107 and 108 (FIG. 10A),paths over which current may flow, illustrated generally at 1003 arerelatively large and the object is perceived as having a large area oris perceived as applying a large force. In the opposite dimension, whena voltage is applied between 111 and 112 (FIG. 10B), the regions overwhich current flow takes place is illustrated generally at 1005, becomerelatively smaller therefore the object would be perceived as having arelatively smaller area or would be perceived as providing a relativelysmaller force.

If the system is programmed to the effect that the object has a constantarea and applies a constant force, these differences in terms of currentflow may be processed in order to given an indication as to theorientation of the object. Thus, the system of the type illustrated inFIGS. 10A-10B, is used in combination with the detector of the typeillustrated in FIG. 9 it is possible to make reference to the parametersof location in two-dimensions, force or pressure, the area ofapplication and orientation.

In the preferred embodiment, electrical characteristics of voltage andcurrent are measured. Alternatively, it would be possible to determinethe resistance or the resistivity of the conducting sheets. Problems maybe encountered when using alternating currents due to energy beingradiated from the conducting sheets. However, in some situations it maybe preferable to use alternating currents, in which further electricalcharacteristics of the detector may be considered, such as capacitance,inductance and reactance etc.

The detector shown in FIG. 1, constructed from conducting planes 102 and103, operates satisfactorily if the plane of the detector is maintainedsubstantially flat. This does not create a problem in many applicationswhere relatively flat operation is considered desirable. However,although constructed from fabric, thereby facilitating bending andfolding operations, the reliability of the detector in terms of itselectrical characteristics cannot be guaranteed if the detector planesare folded or distorted beyond modest operational conditions.

A detector is shown in FIGS. 11A-11B, constructed from fabric havingelectrically conductive elements to define at least two electricallyconductive planes. The detector is configured to produce an electricaloutput in response to a mechanical interaction, as illustrated in FIG.1. At least one of the planes includes first portions and secondportions in which the first portions have a higher resistance than saidsecond portions and the first higher resistance portions are moreflexible than the second portions. In this way, flexing occurs at theportions of high resistance, where contact between the planes has littleeffect, while the lower resistance portions, where contact does have astrong electrical effect, remain substantially rigid such that theflexing of the material does not occur over these portions of thedetector.

Portions 1101 have a relatively high resistance compared to portions1102. Portions 1101 are not involved in terms of creating an electricalreaction in response to a mechanical interaction. The electricalresponses are provided by the more rigid weave of portions 1102. Thepurpose of portions 1101 is detailed in FIG. 11B. A curvature has beenapplied to the detector but the configuration is such that normaloperation is still possible. The flexing has occurred predominantly atportions 1101. However, portions 1102 have remained straight therebyensuring that they remain displaced from each other, even when acurvature is present, such that the detector is still available fordetecting the presence of a mechanical interaction.

The rigidity of portions 1102 may be enhanced as shown in FIG. 12A. Afirst plane 1201 has rigid portions 1202 and flexible portions 1203. Asecond plane 1204 has relatively rigid portions 1205 and relativelyflexible portions 1206. The relatively flexible portions 1206 physicallycontact against similar portions 1203 in the first plane 1201. In orderto ensure that there is no, or at least minimal electrical interactionat these points of contacts, the electrical resistance of the flexibleportions 1203 and 1206 is relatively high. A partially insulating layermay be provided between the conducting layers, as shown in FIG. 1.However, the flexible portions 1203 act as insulating separatorstherefore in this embodiment the provision of a separation layer is notessential. Furthermore, the rigidity of the interacting sections, interms of the rigid portions 1202 and 1205, has its rigidity furtherenhanced by the presence of relatively solid intermediate plates 1208.

Flexing of the construction shown in FIG. 12A is substantially similarto that provided by the embodiment shown in FIG. 11B. The flexing of theembodiment shown in FIG. 12A is detailed in FIG. 12B. Flexing occurs atthe position of the relatively flexible portions 1203 and 1206. Therigidity of portions 1202 and 1205 is enhanced by the provision of moresolid plates 1208. Thus, the embodiment shown in FIGS. 12A and 12B mayhave more strenuous flexing forces applied thereto such that mechanicalinteraction detection is maintained even under severe operatingconditions.

The provision of the flexible portions effectively provide lines overthe surface of the conducting planes where folding is permitted. Thus,complex curvatures may be obtained by a number of folds being effectedat a plurality of these preferred foldable lines, thereby allowingcomplex shapes to be attained while maintaining the desired electricalcharacteristics.

An alternative embodiment is shown in FIG. 13 in which a firstco-operating plane has flexible high resistive portions 1301 and rigidconducting portions 1302. This plane co-operates with a second plane1303 of substantially homogenous construction. Thus, sufficient flexingand insulation is provided by the non-conducting flexible portions 1301of the lower co-operating plane 1304. The rigidity of conductingportions 1302 may be enhanced in a fashion substantially similar to thatprovided by FIG. 12A as illustrated in FIG. 14. The device includes anouter plane 1401 of substantially homogenous conducting construction.Below this, there is provided a second co-operating plane 1402 and thetwo planes may be separated by an insulating layer not shown in theexample. The second plane or layer includes flexible non-conductingportions 1403 and more rigid conducting portions 1404, substantiallysimilar to those shown in FIG. 13. In addition, rigid plates 1405 areprovided below each rigid portion 1404 thereby significantly enhancingthe rigidity of these portions. Thus, the construction in FIG. 14 iscapable of withstanding more aggressive working environments compared tothe lighter construction shown in FIG. 13. In the construction shown inFIGS. 13 and 14 the outer layers, 1303 and 1401 respectively, arefabricated in a substantially elastic fashion, thereby providing for astretching or extension of this layer during flexing operations.

The detector shown in FIG. 1 is capable of accurately detecting theposition of a mechanical interaction and as previously described, it isalso possible to determine other characteristics of the mechanicalinteraction by modifying other electrical properties. A problem with thedetector shown in FIG. 1 is that it experiences difficulties if morethan one unconnected mechanical interaction takes place. If a firstmechanical interaction were to take place and, simultaneously, a secondmechanical interaction were to take place, displaced from the first, itwould not be possible, using the configuration shown in FIG. 1, toidentify the presence of two mechanical interactions. A condition wouldbe detected to the effect that a mechanical interaction is taking placebut the system would tend to perceive this as a single mechanicalinteraction having characteristics substantially similar to the averageof the characteristics of the two independent interactions.

An alternative embodiment for overcoming problems of this type is shownin FIG. 15. In FIG. 15, a plurality of detectors 1501, 1502, 1503, 1504,1505, 1506 and 1507 have been connected together and each of theseindividual detectors has its own unique connectors 1511, 1512, 1513 and1514. In this way, each of the individual detectors may be connected toits own respective control circuit, such as circuit 121 shown in FIG. 1or, in an alternative embodiment, a single control circuit of the typeshown in FIG. 1 may be shared, using a switching arrangement, betweenall seven of the individual combined detectors. In this way, eachindividual detector, such as detector 1501, provides the same level ofaccuracy as the detector shown in FIG. 1. However, if two or moremechanical interactions take place on different detector sections, it ispossible to detect this condition and provide appropriate outputresponses. However, it is only possible to detect a plurality ofmechanical interactions if these interactions take place on differentsections and it is not possible for the embodiment shown in FIG. 15 todetect a plurality of interactions if these interactions take place onthe same section.

In the arrangement shown in FIG. 15, the detectors have been arranged instrips such that there is enhanced definition in the direction of arrow1521 but the definition in the direction of arrow 1522 has not changed.

In the detector shown in FIG. 1, position detection is made possibleusing four electrical connection cables, a first two connected toopposing diagonal corners of the upper sheet and a further two connectedto the alternative opposing diagonal corners of the lower sheet. Analternative configuration is shown in FIG. 16 in which electricalconnectors 1601, 1602, 1603 and 1604 are connected to respective corners1611, 1612, 1613 and 1614 of a lower plane conducting sheet 1621. Anupper plane conducting sheet 1622 is connected to a single detectingcable 1631 connected at a position 1632 towards an edge of upperconducting sheet 1622. A disadvantage of the configuration shown in FIG.16 is that five separate electrical connections are required whereasonly four electrical connections are required in the configuration shownin FIG. 1. However, in some circumstances, the configuration shown inFIG. 16 does have advantages over that shown in FIG. 1.

The configuration shown in FIG. 16 may be used to effectively multiplexthe operation of a detector so as to facilitate the detection of aplurality of mechanical interactions to a greater extent than theconfiguration shown in FIG. 15. In particular, it facilitates detectingmultiple mechanical interactions in both dimensions of the planardetector.

As shown in FIGS. 17A and 17B, a lower planar sheet 1701 (FIG. 7A) hasconnections 1702, 1703, 1704 and 1705 at each of its corners. Thus,sheet 1701 operates in a way which is substantially similar to theoperation of sheet 1621 and all output voltages are generated withinthis sheet, either across diagonal 1702 to 1704 or across diagonal 1703to 1705, thereby giving a two-dimensional co-ordinate within the area ofthe sheet.

An upper planar sheet 1721 (FIG. 17B) is divided into a plurality ofportions, in the example shown, eight portions 1731 to 17389 areprovided. Thus, the mechanical action results in conducting planes of atleast one of said regions being brought into electrical interaction withthe lower plane 1701. Furthermore, if a mechanical interaction occurs atregion 1731 and a second mechanical interaction occurs at region 1735(for example) both of these mechanical interactions may be determinedindependently and an output to this effect may be generated by aprocessing system, such as system 131.

In order to achieve the space division multiplexing provided by regions1731 to 1738, time division multiplexing of the electrical signals isperformed in which, during each individual time slot, one individualregion 1731 to 1738 is considered. This is achieved by each individualregion 1731 to 1738 having its own respective electrical connector 1741to 1748. These connectors are preferably incorporated in to thestructure of the sheet.

Control circuitry for the configuration shown in FIGS. 17A-17B requiresmodification compared to that shown in FIG. 2. In particular, each ofthe eight output control lines 1741 is supplied to its own respectivebuffering amplifier, similar to amplifiers 222 and 223 and the outputfrom each of these eight amplifiers is applied to appropriate switchingdevices, allowing one of eight inputs to be selected using a pluralityof switches substantially similar to switch 221.

A complete scanning cycle consists of applying a voltage between inputterminals 1702 and 1704. An output is then considered from eachindividual output terminals 1741 to 1748. The voltages are then reversedsuch that a voltage is applied between output terminals 1705 and 1703.Each of the individual input terminals is then considered again so as toprovide two-dimensional co-ordinates within each of the individualregions 1731 to 1748. As described with respect to FIG. 2, both voltagesand currents may be considered in order to provide additionalmechanically related information, such as pressure related informationetc.

In the detector configuration shown in FIG. 1 and in alternativedetector configurations, such as that shown in FIG. 15 and that shown inFIG. 16, it is necessary to provide electrical connection betweenprocessing equipment and the detector fabric itself. Techniques for theaddition of electrical connectors to current conveying fabrics areknown. However, in the known techniques, continual wear and usage of thedetector assembly often results in electrical connectors becomingdisconnected from the material fabric, resulting in total systemfailure. It is therefore highly desirable to provide a system in whichthe electrical connector is held very securely to the material fabricitself so as to provide a robust system which does not becomedisconnected through continual use.

An improved approach to providing electrical connection to the electriccurrent carrying conductors within the fabric is illustrated in FIG. 18.Further modification is shown in FIG. 19. In both of these systems, thefabric is constructed from electrically conducting fibres and fromelectrically insulating fibres by a mechanical process, such as weavingor knitting. An improved electrical connection is achieved by connectingelectrical connection devices to the electrically conducting fibres ofthe fabric forming the detector during the mechanical fabric generatingprocess. Thus, in the embodiments shown in FIG. 18 and FIG. 19, there isno requirement for adding connectors after a fabric has been created.The provision of a connector to the electric current carrying fibres isachieved during the actual mechanical process itself. Thus, for example,if the fibres are being produced by a knitting operation, part of thisknitting operation involves procedures by which the electrical currentcarrying connector is actually included as part of the overall knit.

Fibres 1801 making up the weave are illustrated in FIG. 18. A weavingprocedure may be considered as generating woven fabric by traversing inthe direction of arrow 1802. At pre-programmed positions, or at manuallyselected positions, modifications are made to the weaving process to theeffect that a connector 1803 is to be introduced.

In the example shown in FIG. 18, connector 1803 is an insulationdisplacement connector (IDC) allowing an insulated wire to be connectedin such a way that it is not necessary to remove the insulation from thewire, given that the insulation is effectively cut as the wire,illustrated by reference 1804 is inserted into the connector in thedirection of arrow 1805.

The weaving procedure is modified such that connector 1803 is includedas part of the weave and is thereby held relatively firmly after theweaving procedure has been completed. In order to provide a furtherenhanced mechanical connection between electrical connector 1803 and theremaining woven fabric, additional layers of electrically conductingepoxy resin 1805 and 1806 are applied, such that, in operation, physicalforce applied to connector 1803 will not, under normal circumstances,displace connector 1803 from the woven material of the device andelectrical integrity of the device will be maintained.

A similar configuration is shown in FIG. 19 in which a rivet fastener1901 is applied during a weaving or knitting process, therebysubstantially embedding the rivet fastener within the overall weave orknit. After the rivet fastener has been secured by the woven fabric1902, electrically conducting epoxy resin 1903 is applied to provideenhanced mechanical and electrical stability.

In the configuration shown in FIG. 1 and in the configuration shown inFIG. 16, an electrical field is established over the transmitting plane.Given a plane of infinite size, the electrical field would have aregular geometric distribution and the position of a mechanicalinteraction could be determined from two voltage measurements in asubstantially straightforward way. However, in the configuration shownin FIG. 1 and FIG. 16, edges are present and these edges introducesevere distortions to the nature of the electric field from whichmeasurements are being taken. In the control circuit 121 and within thedata processing system 131 it is possible to provide a level ofcompensation, possibly in response to empirical measurements but such anapproach has disadvantages, one of which being a loss of resolution.

Systems are shown in FIGS. 20 and 21 in which a detector is constructedfrom fabric having electrically conductive elements to define at leasttwo electrically conducting planes. The detector is configured toproduce an electrical output in response to a mechanical interaction.The relationship between mechanical interaction and electrical output isenhanced by introducing a conductivity non-uniformity which is includedin at least one of the planes so as to modify an electrical response tothe mechanical interaction.

In FIG. 20, an electrical connector 2001 is connected to a plane at afirst corner and a second connector 2002 is connected to the diagonallyopposing corner. A configuration of this type could be used for adetector of the type shown in FIG. 1, in which the electrical fieldeffectively traverses across the diagonal corners, resulting indistortions at the edges. In the embodiment shown in FIG. 20, aconducting thread 2003 with relatively low resistivity is includedacross edge 2004, electrically connected to connector 2001. Similarly, asecond conducting thread 2005, with relatively low resistivity, extendsfrom electrical connection 2002 along edge 2006. In this way, the wholeof edge 2004 becomes conducting and the whole of edge 2006 becomesconducting. The resulting electric field is then substantially linearthroughout the length of the detector thereby substantially eliminatingnon-linear edge effects.

In its co-operating plane 2010 a low resistance conducting thread 2011is included along edge 2012 and a similar conducting thread is providedalong the opposing edge. In this way, the electric field traverses in adirection which is orthogonal to the electric field provided in theupper sheet, thereby allowing co-ordinates defined in mutuallyorthogonal coordinate space.

A conducting material is shown in FIG. 21 in which areas 2101, close toall four edges, have had their conductivity modified, such that theoverall conductivity of the sheet is non-uniform. This modification toconductivity may be achieved in several ways, including the addition ofa conducting thread of the type illustrated in FIG. 20. Alternatively,the modification to conductivity, to provide conductivitynon-uniformity, may be achieved by a printing operation in whichelectrically conducting inks, possibly including silicon, are printed atregion 2101. Alternatively, the density of conducting fibres in thewoven material itself may be modified towards the edges of the detector,again resulting in a conductivity non-uniformity. Furthermore, it shouldbe appreciated that modifications of this type may be achieved usingcombinations of the above identified effects in order to tailor therequired level of non-uniformity for a particular application.

In the configuration shown in FIG. 1, a cycle is performed in whichupper plane 102 effectively transmits allowing signals to be received bylower plane 103. A co-ordinate position is identified by reversing theoperation of these planes, such that certain parts of the cycle includesituations in which the lower plane 103 is effectively transmitting andthe upper plane 102 is effectively transmitting. In a configuration ofthis type, it is preferable for the material types to be similar so asto provide substantially similar operations when plane 102 istransmitting or when plane 103 is transmitting. This is a particularlyimportant constraint when the system is being used to measure currentflow, given that different resistivities could be achieved in thedifferent directions of current flow.

In the configuration shown in FIG. 16, transmission always occurs fromplane 1621, although in different orientations, and detection alwaysoccurs from plane 1622. With a configuration of this type, currentalways flows in the same direction therefore it is not essential forplanes 1621 and 1622 to have equivalent mechanical constructions.

In the configuration shown in FIG. 16, a detector is constructed fromfabric having electrically conductive elements to define at least twoelectrically conductive planes and configured to produce an electricaloutput in response to a mechanical interaction. A second electricallyconductive plane, such as plane 1622 of the detector, has at least oneelectrical characteristic that differs significantly in value from thevalue of said characteristic of the first plane 1621.

In the detector shown in FIG. 16, the upper receiving plane 1622 has asignificantly lower resistance than the lower transmitting plane 1621.In this way, as the area of mechanical interaction increases, the amountof current flow increases significantly, thereby improving thedefinition of the system with respect to changes in the size of themechanical interaction, and allowing for less intensive calculationswhen determining force etc.

What is claimed is:
 1. A position detector constructed from fabrichaving a first electrically conductive fabric plane and a secondelectrically conductive fabric plane, wherein a plurality of wires areconnected to said first plane so as to establish at least one electricalpotential gradient across said plane; a mechanical interaction bringssaid first electrically conducting plane into contact with said secondelectrically conducting plane such that current flows at the position ofsaid contact; a single wire is connected to said second plane so as toallow said current to flow; and the resistivity of said first plane ishigher than the resistivity of said second plane so as to facilitate theestablishment of a potential gradient across said first plane and tofacilitate current flow through said second plane.
 2. A positiondetector according to claim 1, wherein four wires are connected to saidfirst plane, such that a first wire and a second wire create a potentialgradient in a first direction and a third wire and a fourth wire createa potential gradient in a second direction.
 3. A detector according toclaim 2, wherein the degree of current flow is indicative of appliedforce.
 4. A detector according to claim 1, wherein the degree of currentflow is indicative of an area of contact.
 5. A detector according toclaim 1, wherein said fabric has electrically conducting fibres andelectrically insulating fibres; and electrical connection means areconnected to said electrically conducting fibres of said fabric during amechanical weaving or knitting process.
 6. A detector according to claim1, wherein a conductivity non-uniformity is included in said first planeso as to modify the electrical response to a mechanical interaction. 7.A method of manufacturing a position detector constructed from fabric,comprising the steps of connecting a plurality of wires to a firstfabric conducting plane such that said plane is configured to have anelectrical potential gradient established throughout said plane;attaching a single wire to a second fabric electrically conductingplane; displacing said first fabric from said second fabric so as toestablish a position detector; and connecting detection apparatus tosaid wires so as to measure current when a mechanical interaction bringssaid first plane and said second plane into contact, wherein theresistivity of said first plane is higher than the resistivity of saidsecond plane so as to facilitate the establishment of a potentialgradient across said first plane and to facilitate current flow throughsaid second plane.
 8. A method according to claim 7, wherein four wiresare connected to said first plane.